Cellulosic metallic laminates



United States Patent U.S. Cl. 161-214 Claims ABSTRACT OF THE DISCLOSUREAdhesive compositions comprising casein, a metallic oxide, diammoniumphosphate with or without natural and synthetic polymeric materials.Laminates represented by cellulosic-metallic laminates with adhesiveinterposed between the layers are disclosed.

This application is a division of my copending U.S. application Ser. No.232,885 filed Oct. 24, 1962 now Patent Number 3,375,121.

This invention relates to the manufacture of an adhesive and toprocesses for the production of said adhesive. The resulting adhesive isparticularly valuable for the production of cellulosic and foilcombinations for the wrapping of food products, and making of bottlelabels, etc.

Casein adhesives have been used satisfactorily for the gluing of woodand as a base for preparing coating compounds of paper. However, caseinshows very little adhesive properties when applied to metals or whenused as an adhesive between cellulosic materials such as cloth or paperand metal such as tin or aluminum foil. Casein solutions containingfluorine compounds have been used to bond cellulosics to metal, butfilms cast from such solutions are quite sensitive to water.Furthermore, casein solutions containing ammonium, zinc or magnesiumsilicofiuorides, as well as alkali-metal fluorides and alkali metal andammonium fiuoborates, are to a certain extent toxic.

Generally, casein solutions are prepared by dissolving the casein withan alkali such as monovalent metal oxides or hydroxides, but suchsolutions do not maintain a stable viscosity upon aging. Multivalentmetal salts form water insoluble caseinates which consequently gel uponaging. Even the peptizing agents, for example, urea, do not producecasein solutions of stable viscosity as such solutions either thin outor body up on storage, depending on the concentration of the peptizerand the heat treatment used in their preparation. Sodium naphthalenesulfonate has been used to produce viscosity-stable casein solutions,but dry films of this adhesive are soluble in cold water. in addition,phosphates have been used in casein solutions, but such solutions alsohave unstable viscosity.

Accordingly, it is an object of this invention to produce caseinadhesive fihns of which when air-dried are waterresistant.

It is also an object of this invention to produce an adhesive which hasviscosity stability and is nontoxic.

A further objectof this invention is to manufacture an adhesive basewhich is compatible with both the low and high pH resin latices.

A still further object is to provide a process for producing an adhesivewhich has the above-mentioned properties.

Additional objects of this invention include the production of laminatesand especially laminates of cellulosic materials with metal foil.

Additional objects, if not specifically set forth herein, will bereadily apparent to those skilled in the art from the detaileddescription of the invention which follows.

In general, this invention comprises dissolving casein in an aqueouszinc oxide dispersion using diammonium phosphate as the solvating saltto obtain a water-resistant and viscosity-stable casein adhesive base.Also included within the scope of the invention are adhesive emulsionsproduced by the blending of high and low pH resin latices with thecasein adhesive base. These casein-resin emulsions are excellentadhesives for bonding metallic surfaces to cellulosics and suchemulsions are also viscosity-stable and water-resistant.

More specifically, the adhesive base comprises casein (either rennetcasein or acid-precipitated casein), zinc oxide or a mixture of zincoxide and aluminum oxide, and diammonium phosphate either alone or incombination with preservatives, defoamers, plasticizers, solvents,antioxidants, curing agents, accelerators, pigments, fillers,stabilizers, etc. The adhesive compositions are easily prepared bydispersing zinc oxide or a mixture of zinc oxide and aluminum oxide inwater with agitation, followed by the addition of the casein. Themixture is stirred or agitated until the casein is thoroughly wetted.Diammonium phosphate is then added and usually followed by the additionof a preservative for the casein and if desired a defoamer. The mixtureis heated to a temperature between about and 200 degrees Fahrenheit,preferably between about to degrees Fahrenheit, in order to solubilizethe casein.

Generally, the zinc oxide should be present in amounts of between one to12.5 parts, preferably 3 to 7 parts, by weight to every 100 parts ofcasein employed. The amount of diammonium phosphate will normally rangebetween 10 to 37.5 parts, preferably l522 parts, by weight based upon100 parts of casein. At this point, it may be mentioned that thediammonium phosphates may be made in situ by adding ammonia to the zincoxide-casein solution, followed by the addition of dilute phosphoricacid. Preferably, the zinc oxide and diammonium phosphate are utilizedin such a ratio as to obtain a casein solution having a pH in the rangeof 5.3 to 8.8. Part of the ZnO can be replaced with hydrated aluminumoxide. For example, 3 parts of ZnO and 2 parts of A1 0 per 100 parts ofcasein. Aluminum oxide alone can be used but zinc oxide is preferredinasmuch as straight aluminum oxide gives quite low viscosity caseinsolutions, and low viscosity blends with the resin emulsions. The amountof water utilized in the system is limited only by the viscositydesired.

Utilization of zinc oxide for water resistance of casein adhesives isknown, but such solutions have an unstable viscosity. Likewise,phosphates have been used to make casein solution, but such solutionsalso lose their viscosity. It was, therefore, quite surprising andthoroughly unexpected to discover that the incorporation of smallamounts of zinc oxide in conjunction with diammonium phosphate wouldgive a viscosity-stable casein solution. While applicant does not intendto be bound by any particular theory, and while the mechanism is notcompletely clear, it is thought that the zinc forms some sort of azincammonia complex, which, in turn, reacts with the casein, rendering aviscosity-stable solution having a pH range of between about 5.0 to 9.0.The diammonium phosphate appears to be unique since other dibasicphosphates such as disodium or dipotassium phosphate, etc., do not holdthe zinc and the zinc oxide is precipitated out in a short time. Also,the zinc oxide is precipitated out of blends of casein solutions andresin latices in the absence of the diammonium phosphate.

The present invention also provides for the addition of emulsions ofpolymers having a wide range of high molecular weight to the caseinadhesive bases. Such high molecular weight resins include the natural orsynthetic resins and/or natural or synthetic rubbers and the like.

To the casein adhesive base there may be added one or more of theelastomers in an emulsion form, such as natural rubber latex, Butylrubber, Buna S, Perbunan latex, neoprene latex, Vistanex (isobutylene),styrene-butadiene latex, polyvinyl alcohol, and Thiokol (prepared fromethylene dichloride and sodium polysulfide). Other synthetic polymerssuch as the alkadienes-acrylonitrile copolymers(butadiene-acrylonitrile), the polymerized olefins (polyethylene,polypropylene, polybutylene, etc.), the polyacrylates which includepolymers and copolymers of acrylic and methacrylic acids and their loweralkyl esters such as polymethyl methacrylate and polyethyl acrylate, thevinyl lower carboxylates such as polyvinyl acetate, polyvinyl propionateand polyvinyl butylate and also copolymers of the vinyl lowercarboxylates with the lower alkyl alcohol esters of unsaturated monoanddicarboxylic acids (copolymer of 80% polyvinyl acetate and about 20%dibutyl maleate for example) can be added. Also included are thepolyvinyl halides such as the plasticized and unplasticized polyvinylchlorides (Exon and Geon series), the copolymers of vinyl halides withvinylidene halide or vinyl carboxylates (copolymers of vinyl chloridewith vinylidene chloride or vinyl acetate) the polyvinyl alkyrals suchas the Butvar resins (polyvinyl butyral), the polyvinyl lower alkylethers such as polymethyl vinyl ether, polyethyl vinyl ether, polyvinyln-butyl ether and polyvinyl isobutyl ether, and copolymers of alkylacrylates and vinyl pyrrolidone such as vinyl pyrrolidone-ethyl acrylatecopolymer emulsions. These resins are usually emulsified or dispersed inwater and the colloidal suspension incorporated in the table caseinadhesive base. In general, the amount of resin in the blends will rangefrom 33-400 parts of resin emulsion (40-60% solid) for every 100 partsof casein base. As can be seen by the list of the above resins, thecasein adhesive solutions of this invention are compatible with both thelow pH resin latices and with the high pH or alkaline resin emulsions.Neoprene latex is the preferred olymeric resin for emulsion with theadhesive.

The casein adhesive bases of the instant invention can also be used asan emulsifying and stabilizing agent in making various emulsions.Hard-to-emulsify resins such as polyethylene can be emulified with theaid of this particular casein solution. Other polymeric resins of thenonelastomer type, in the emulsions form, may be utilized in the presentinvention. Included are the vinyl resins, melamine resins, ureaformaldehyde resins, vinsol resins, rosin, and rosin esters, phenolmodified resins and the like. If at any time it is desirable to lowerthe pH range of the casein-resin solution, dilute phosphoric acid ormonoammonium phosphate may be added.

The mixtures of the casein adhesive solution in various proportions withthese resin emulsions produce most useful viscosity-stable adhesiveswhich can be utilized for foil laminating, wood bonding such as themaking of plywood, etc. The adhesive is especially valuable for theproduction of foil and paper combinations for the wrapping of foodproducts. The adhesive adheres quickly and satisfactorily and yields astrong bond when dried. Furthermore, the bond does not deteriorate toany extent when the laminate is rewetted. Also, the laminated paper-foilsheets can withstand folding, and does not delaminate at elevatedtemperatures.

The following examples are presented to illustrate the invention. Itwill be understood that these example are illustrative and should not betaken in any manner as limiting the invention as defined in the appendedclaims.

EXAMPLE I A solution was prepared by dispersing, with good agitation, 4parts of zinc oxide in 440 parts of water. To this mixtures was added 82parts of casein and the system stirred until all the casein wasthoroughly wetted. Then 16 parts of diammonium phosphate was added,followed by the addition of preservatives. The preservatives consistedof 2 parts of Dowicide A (sodium orthophenylphenate), and 2 parts ofDowicide G (sodium pentachlorophenate). The mixture was heated to atemperature of about 180 P. so as to solubilize the casein, theresulting adhesive having a pH of about 7.0.

EXAMPLE II A casein solution was prepared by stirring 4 parts of zincoxide and parts casein into 400 parts of water. 14.7 parts of a 28%ammonia solution, 3 parts of Dowicide A and 3 parts of Dowicide G werethen added and the mixture heated to 175 F. to solubilize the casein. Anadditional 40 parts of water, along with 14 parts of an phosphoric acidsolution were added so as to react with the ammonia to form thediammonium phosphate in situ. To this material there may be added asuspension of a high molecular weight resin; for example, a naturalrubber latex in the amount of 50 to 200 parts by weight per 100 parts ofcasein base.

EXAMPLE HI To 100 parts of the casein adhesive base of Example I therewas added 100 parts of neoprene latex (polymerized chloroprene). Theresultant system had a pH of 8.5 and a viscosity for 3,000 cps. Thismaterial was applied in the usual way to a sheet of aluminum foil andcovered with a sheet of paper. The laminate was rolled and dried quicklyby heat. After cooling the foil was torn from the paper by peeling. Theadhesive gave a 100% paper fiber failure. It had very little tendency tofoam, and machined very well and was quite easy to clean up.

EXAMPLE IV A similar mixture utilizing 100 parts of Darex B (a copolymeremulsion of about 80% polyvinyl acetate and 20% dibutyl maleate andhaving about 55% solids) and 100 parts of the casein base produced as inExample I was blended together. The adhesive blend was an excellent foiladhesive producing an excellent paper fiber failure.

EXAMPLE V An excellent aluminum foil-paper laminate was produced byusing 800 parts of natural rubber latex, 800 parts of the caseinadhesive base, and 70 parts of a 20% monoammonium phosphate solution.The monoammonium phosphate was added to bring the final pH of the systemdown from 9.0 to 6.8. The viscosity of the laminating adhesive was 1200cps.

EXAMPLE VI An adhesive similar to that of Example V was prepared byusing 1,000 parts of GRS latex (a copolymer of 1,3-butadiene andstyrene), 800 parts of the casein base and 30 parts of a 20%monoammonium phosphate solution. This adhesive had a pH of 6.8, aviscosity of 25 cps. and had excellent foil adhesive properties andwater resistance.

EXAMPLE VII Another foil laminating adhesive was produced by using 100parts of Rhoplex B-lO (an acrylic emulsion containing about ethylacrylate and some methyl methacrylate and having about 45% solids) and80 parts of the casein base produced in accordance with Example II. Thematerial shows an excellent dry and wet strength when used as a cementbetween paper and aluminum foil.

EXAMPLE VIII A good word-working adhesive was produced by blending partsof Elvacet 81-900 (a 55 solids p y y acetate emulsion), 10 parts ofdibutyl phthalate and 100 parts of the casein base produced inaccordance with Example II. This formula was used in bonding plywood andshowed high initial and aged strengths, as well as very good resultswith paper and foil.

The above adhesive combinations can be used to laminate metallicsurfaces to cellulosics in general and specifically aluminum, tin andcopper foil to paper for use in food packaging, beer bottle labels, inlaminated wrappings for cigaretts and gum, etc. They can also be used tobond wood, glass, leather, plastics, etc. In addition, the resultingcompositions possess excellent stability, have little tendency to foam,have good machining properties and are relatively easy to clean up.

Any of the conventional modifiers such as defoamers, plasticizers,organic solvents, antioxidants, curing agents, accelerators, pigments,dyes, fillers or stabilizers may be added to the casein adhesive base orthe foil laminating compositions without ailecting the nature of theproduct or the process of making it.

I claim:

1. A cellulose-metallic laminate comprising, in combination, a metalliclayer and a cellulosic layer with an interposed adhesive therebetweenwhich is strongly adherent to both the metallic and the cellulosiclayers comprising, a casein solution, a member selected from the groupconsisting of zinc oxide, aluminum oxide and mixtures thereof,diammonium phosphate and an aqueous emulsion of a material selected fromthe group consisting of natural and synthetic elastomers.

2. The laminate of claim 1 wherein the metallic layer is aluminum foiland the cellulosic layer is paper.

3. The laminate of claim 1 wherein the metallic layer is selected fromthe group consisting of aluminum foil, copper foil and tin foil.

4. The laminate of claim 1 wherein the elastomer is a neoprene latex.

5. The laminate of claim 1 wherein the elastomer is a member selectedfrom the group consisting of natural rubber, neoprene, styrene-alkadienecopolymers, alkadiene-acrylonitrile copolymers, polyvinylalcohol,polyvinylhalides, polyvinylidene halides, polyvinyl ethers, polyvinylalkyrals, polyvinyl pyrrolidones, polyacrylates, polymerized olefins,ethylene polysulfide polymers, polyvinyl carboxylates and copolymers ofpolyvinyl carboxylates and alkyl esters of unsaturated acids.

6. The laminate of claim 1 wherein the elastomer is a copolymer emulsionof polyvinyl acetate and dibutyl maleate,

7. The laminate of claim 1 wherein the cellulosic layer is paper, theelastomer is a neoprene latex and the metallic layer is selected fromthe group consisting of aluminum foil, copper foil and tin foil.

8. The laminate of claim 1 wherein the casein solution contains about 1to about 12.5 parts by weight of a member selected from the groupconsisting of zinc oxide, aluminum oxide, and mixtures thereof, about 10to about 37.5 parts by weight of diammonium phosphate per parts of saidcasein, and including from about 33 to about 400 parts by weight per 100parts casein of an aqueous emulsion of a material selected from thegroup consisting of natural and synthetic elastomers.

9. The laminate of claim 8 wherein the elastomer is a neoprene latex andthe cellulosic layer is paper.

10. The laminate of claim 8 wherein metallic layer is selected from thegroup consisting of aluminum foil, copper foil and tin foil, theelastomer is selected from the group consisting of natural rubber latexand neoprene latex and the cellulosic layer is selected from the groupconsisting of paper, wood and cloth.

References Cited UNITED STATES PATENTS 2,346,812 4/1944 Bradner 117-1562,482,917 9/1949 Kaplan 106-146 2,933,469 4/1960 Depew 260-8 3,053,6769/1962 Higbee 106-148 3,166,523 1/ 1965 Weinheimer 260-8 r HAROLDANSHER, Primary Examiner a R. A. KILLWORTH, Assistant Examiner US. Cl.X.R.

